Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.36   7.805%   $267.7445   $267.74   $267.75   $267.70  
  Purchase #2 $143.61   6.784%   $153.3525   $153.35   $153.35   $153.40  
  Purchase #3 $130.52   10.269%   $143.9231   $143.92   $143.90   $143.90  
  Purchase #4 $219.47   7.374%   $235.6537   $235.65   $235.65   $235.70  
  Purchase #5 $165.70   12.842%   $186.9792   $186.98   $187.00   $187.00  
  Purchase #6 $172.39   12.383%   $193.7371   $193.74   $193.75   $193.70  
  Purchase #7 $53.56   5.863%   $56.7002   $56.70   $56.70   $56.70  
  7 purchase totals = $1,133.61       $1,238.0903   $1,238.08   $1,238.10   $1,238.10