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 $184.57   10.379%   $203.7265   $203.73   $203.75   $203.70  
  Purchase #2 $82.74   13.397%   $93.8247   $93.82   $93.80   $93.80  
  Purchase #3 $80.33   13.303%   $91.0163   $91.02   $91.00   $91.00  
  Purchase #4 $146.55   13.188%   $165.877   $165.88   $165.90   $165.90  
  Purchase #5 $239.62   3.126%   $247.1105   $247.11   $247.10   $247.10  
  Purchase #6 $124.52   8.476%   $135.0743   $135.07   $135.05   $135.10  
  Purchase #7 $80.47   13.489%   $91.3246   $91.32   $91.30   $91.30  
  7 purchase totals = $938.80       $1,027.9539   $1,027.95   $1,027.90   $1,027.90