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 $105.84   10.331%   $116.7743   $116.77   $116.75   $116.80  
  Purchase #2 $248.98   9.873%   $273.5618   $273.56   $273.55   $273.60  
  Purchase #3 $160.65   6.494%   $171.0826   $171.08   $171.10   $171.10  
  Purchase #4 $70.39   7.108%   $75.3933   $75.39   $75.40   $75.40  
  Purchase #5 $124.98   7.644%   $134.5335   $134.53   $134.55   $134.50  
  Purchase #6 $22.92   5.670%   $24.2196   $24.22   $24.20   $24.20  
  Purchase #7 $246.93   4.338%   $257.6418   $257.64   $257.65   $257.60  
  7 purchase totals = $980.69       $1,053.2069   $1,053.19   $1,053.20   $1,053.20