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 $91.94   5.202%   $96.7227   $96.72   $96.70   $96.70  
  Purchase #2 $240.65   4.484%   $251.4407   $251.44   $251.45   $251.40  
  Purchase #3 $247.33   7.597%   $266.1197   $266.12   $266.10   $266.10  
  Purchase #4 $24.64   8.642%   $26.7694   $26.77   $26.75   $26.80  
  Purchase #5 $201.77   5.107%   $212.0744   $212.07   $212.05   $212.10  
  Purchase #6 $93.31   4.846%   $97.8318   $97.83   $97.85   $97.80  
  Purchase #7 $49.29   6.137%   $52.3149   $52.31   $52.30   $52.30  
  7 purchase totals = $948.93       $1,003.2736   $1,003.26   $1,003.20   $1,003.20