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 $209.33   11.290%   $232.9634   $232.96   $232.95   $233.00  
  Purchase #2 $98.87   11.720%   $110.4576   $110.46   $110.45   $110.50  
  Purchase #3 $202.26   10.740%   $223.9827   $223.98   $224.00   $224.00  
  Purchase #4 $201.52   6.305%   $214.2258   $214.23   $214.25   $214.20  
  Purchase #5 $228.74   7.352%   $245.557   $245.56   $245.55   $245.60  
  Purchase #6 $50.97   4.365%   $53.1948   $53.19   $53.20   $53.20  
  Purchase #7 $30.57   4.261%   $31.8726   $31.87   $31.85   $31.90  
  7 purchase totals = $1,022.26       $1,112.2539   $1,112.25   $1,112.25   $1,112.40