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 $136.65   13.446%   $155.024   $155.02   $155.00   $155.00  
  Purchase #2 $25.85   8.711%   $28.1018   $28.10   $28.10   $28.10  
  Purchase #3 $69.84   5.530%   $73.7022   $73.70   $73.70   $73.70  
  Purchase #4 $189.25   8.190%   $204.7496   $204.75   $204.75   $204.70  
  Purchase #5 $202.28   11.532%   $225.6069   $225.61   $225.60   $225.60  
  Purchase #6 $230.83   6.681%   $246.2518   $246.25   $246.25   $246.30  
  Purchase #7 $235.86   9.608%   $258.5214   $258.52   $258.50   $258.50  
  7 purchase totals = $1,090.56       $1,191.9577   $1,191.95   $1,191.90   $1,191.90