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 $141.36   4.823%   $148.1778   $148.18   $148.20   $148.20  
  Purchase #2 $238.52   13.129%   $269.8353   $269.84   $269.85   $269.80  
  Purchase #3 $11.74   7.300%   $12.597   $12.60   $12.60   $12.60  
  Purchase #4 $152.75   12.347%   $171.61   $171.61   $171.60   $171.60  
  Purchase #5 $120.80   3.819%   $125.4134   $125.41   $125.40   $125.40  
  Purchase #6 $198.56   13.690%   $225.7429   $225.74   $225.75   $225.70  
  Purchase #7 $134.46   11.401%   $149.7898   $149.79   $149.80   $149.80  
  7 purchase totals = $998.19       $1,103.1662   $1,103.17   $1,103.20   $1,103.10