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 $69.76   6.475%   $74.277   $74.28   $74.30   $74.30  
  Purchase #2 $218.29   10.576%   $241.3764   $241.38   $241.40   $241.40  
  Purchase #3 $136.29   10.644%   $150.7967   $150.80   $150.80   $150.80  
  Purchase #4 $30.52   13.755%   $34.718   $34.72   $34.70   $34.70  
  Purchase #5 $200.52   9.424%   $219.417   $219.42   $219.40   $219.40  
  Purchase #6 $69.30   7.179%   $74.275   $74.28   $74.30   $74.30  
  Purchase #7 $220.92   12.241%   $247.9628   $247.96   $247.95   $248.00  
  7 purchase totals = $945.60       $1,042.8229   $1,042.84   $1,042.85   $1,042.90