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 $82.57   10.396%   $91.154   $91.15   $91.15   $91.20  
  Purchase #2 $126.92   9.394%   $138.8429   $138.84   $138.85   $138.80  
  Purchase #3 $150.74   10.556%   $166.6521   $166.65   $166.65   $166.70  
  Purchase #4 $148.55   3.745%   $154.1132   $154.11   $154.10   $154.10  
  Purchase #5 $181.74   10.402%   $200.6446   $200.64   $200.65   $200.60  
  Purchase #6 $60.85   3.474%   $62.9639   $62.96   $62.95   $63.00  
  Purchase #7 $194.99   4.172%   $203.125   $203.13   $203.15   $203.10  
  7 purchase totals = $946.36       $1,017.4957   $1,017.48   $1,017.50   $1,017.50